An Entity-Relationship Diagram (ERD) is a visual representation of data entities, their attributes, and the relationships between them in a database system, aiding in logical database design.

An ERD is a conceptual blueprint that helps database designers plan how data will be structured before implementing a database. It consists of entities (representing tables), attributes (representing columns), and relationships (representing connections between entities). Relationships can be one-to-one, one-to-many, or many-to-many, depending on the nature of data interactions.

For example, in a university database, the Student entity can have attributes like student_id, name, and age, while the Course entity can have attributes like course_id and course_name. The relationship between Student and Course can be many-to-many (i.e., a student can enroll in multiple courses, and a course can have multiple students).

ERDs help developers and database administrators understand data flow, enforce constraints, and improve database efficiency. They are widely used in software development projects to ensure proper database normalization and avoid redundancy.

Example ERD notation:

• Entities: Represented as rectangles
• Attributes: Represented as ovals
• Relationships: Represented as diamonds

[Student] ----(enrolled in)---- [Course]